Analyzer rejects B<X extends A<A<X>>> whereas Dart passes with this.

[iarkh]

Dart SDK Version: 2.1.0-dev.6.0
OS: Windows 10

The following example declares four classes and print their types:

class A<X extends A<X>> {}
class A1<X extends A1<A1<X>>> {}
class B<X extends A<X>> {}
class B1<X extends A<A<X>>> {}

main() {
  print(A);
  print(A1);
  print(B);
  print(B1);
}

Dart passes with this and prints actual types of A, A1, B, B1:

A<A>
A1<A1<A1>>
B<A>
B1<A<A>>
Seems like this is a correct result which corresponds instantiate-to-bound Spec.

However, dartanalyzer throws compile error for class B1<X extends A<A<X>>> here:

error - 'A' doesn't extend 'A<A>' at test.dart:4:22 - type_argument_not_matching_bounds
error - 'X' doesn't extend 'A' at test.dart:4:24 - type_argument_not_matching_bounds
2 errors found.
It should pass here kike dart does.

[eernstg]

Note that there may be some overlap with #34264 (which is focusing on FutureOr, but otherwise similar to this one).

[iarkh]

This bug is still reproducible with the recent dart version:
Dart SDK version: 2.11.0-176.0.dev (dev) (Mon Sep 28 19:05:52 2020 -0700) on "windows_x64"

[eernstg]

Closing: Cf. #43687, we must get a compile-time error for the declaration of B, so the analyzer is behaving correctly. The common front end reports that error as well.